The present invention relates to an electrophotosensitive material which is used for image forming apparatuses such as copying apparatus and the like.
In the image forming apparatuses such as copying apparatus, etc., an organic photosensitive material (OPC) having a sensitivity within the wavelength range of a light source of the apparatus has exclusively been used.
As the organic photosensitive material, there have been known a single-layer type photosensitive material comprising a single-layer type photosensitive layer wherein an electric charge generating material and an electric charge transferring material are dispersed in a membrane of a suitable binding resin, a multi-layer type photosensitive material comprising an electric charge transferring layer containing the above electric charge transferring material and an electric charge generating layer containing an electric charge generating material, which are mutually laminated and the like.
Although those having a high carrier mobility are required as the electric charge transferring material to be used for these photosensitive materials, almost all of electric charge transferring materials having a high carrier mobility are hole transferring materials having hole transferring properties and, therefore, only negative charging type multi-layer type organic photosensitive materials, which are provided with an electric charge transferring layer at their outermost layer from the viewpoint of mechanical strength, are used for practical application. However, since the negatively charged type organic photosensitive material utilizes negative-polarity corona discharge, problems such as large amount of ozone generated, environmental pollution, deterioration of photosensitive material, etc. have arisen.
Accordingly, in order to eliminate the above drawbacks, it has been studied to use an electron transferring material as the electric charge transferring material. In Japanese Laid-Open Patent Publication No. 1-206349, there is suggested that a compound having a diphenoquinone structure is used as the electron transferring material for electrophotosensitive material.
However, it is difficult for electron transferring materials such as diphenoquinones to match with the electric charge generating material, which results in insufficient injection of electrons from the electric charge generating material into electron transferring material. Therefore, sufficient photosensitivity could not be obtained. Further, the single-layer type organic photosensitive layer had a problem that an interaction between diphenoquinone and a hole transferring material inhibits electrons from transferring.
Further, regarding the polarity of the photosensitive material to be charged, the scope of application of the photosensitive material can be widen if one photosensitive material can be used for both positively charged and negatively charged types. Further, if the organic photosensitive material can be used for the single-layer dispersion type, it becomes easy to produce the photosensitive material, thereby preventing generation of a coating defect. Therefore, there are many advantages for improving optical properties.